1, Field of the Invention
The present invention relates to expandable acrylic resin bead impregnated with a physical blowing agent, expanded acrylic resin bead obtained through expansion of the expandable acrylic resin bead, and an acrylic resin molded article obtained by in-mold molding the expanded beads.
2, Description of the Background Art
Conventionally, a foamed molded article has been used as, for example, an evaporative pattern for casting. Specifically, the foamed molded article has been used in a casting process as described below. First, the foamed molded article having a desired shape is embedded in sand, and then a molten metal is poured in the foamed molded article in the sand. At this moment, the foamed molded article thermally decomposes, and is replaced with the molten metal. Then, by cooling the molten metal, a metal casting is obtained.
As the foamed molded article for evaporative patterns, a foamed molded article of expanded styrene resin beads has been used. However, using the foamed molded article of expanded styrene resin beads has a problem related to generation of soot in large amount upon thermal decomposition of the molded article. This soot smears the surface of the casting, and may cause a generation of pinholes inside the casting. The reason for soot generation is thought to be because the styrene resin has aromatic rings. Thus, for the purpose of reducing the generation amount of soot, technologies have been disclosed regarding the usage of, as an evaporative pattern, foamed molded articles made of a polymer of a methacrylic ester not having aromatic rings (cf. Patent Document 1 and Patent Document 2).